Multi-metal oxide ceramic nanomaterial

ABSTRACT

A convenient and versatile method for preparing complex metal oxides is disclosed. The method uses a low temperature, environmentally friendly gel-collection method to form a single phase nanomaterial. In one embodiment, the nanomaterial consists of Ba A Mn B Ti C O D  in a controlled stoichiometry.

STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under Contract No.DE-AR0000114 awarded by the Department of Energy Advanced ResearchProjects Agency-Energy (DOE, ARPA-E). The government has certain rightsin the invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional patent application of U.S. PatentApplication Ser. No. 61/859,447 (filed Jul. 29, 2013), the entirety ofwhich is incorporated by reference.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to bi-metal and multi-metaloxide ceramics.

Functional ceramics have been a research focus due to their wideapplications in the electronic industry. With the requirements ofminiaturization, integration and sustainable development, greentechnologies of low energy consumption, environmentally friendlysynthesis and new materials with distinguished properties and beingprintable are drawing more and more attentions. Ferroic inorganic solidsfind utility across a broad range of applications in the electronicsindustry because of magnetic and electrical properties. Multiferroicsrepresent an outstanding twenty-first century challenge toward nextgeneration electronics but progress is limited by physical restrictionson the co-existence of substantive magnetic or electrical performance inknown compounds. Single phase oxides that contain three or more metalsprovoke excitement in structure and property discovery, especially wherethe properties are remarkable. Additional functional ceramics aretherefore desirable.

The discussion above is merely provided for general backgroundinformation and is not intended to be used as an aid in determining thescope of the claimed subject matter.

BRIEF DESCRIPTION OF THE INVENTION

A convenient and versatile method for preparing complex metal oxides isdisclosed. The method uses a low temperature, environmentally friendlygel-collection method to form a single phase nanomaterial. In oneembodiment, the nanomaterial consists of Ba_(A)Mn_(B)Ti_(C)O_(D) in acontrolled stoichiometry.

In a first embodiment, a method for producing a metal oxide ceramicnanomaterial is disclosed. The method comprising steps of mixing a firstmetal-organic salt comprising a first metal (M¹) and a secondmetal-organic salt comprising a second metal (M²) in an anhydroussolvent to form a first intermediate, wherein M¹ and M² areindependently selected from the group consisting of barium, manganese,titanium, iron, nickel, copper, bismuth, cobalt, samarium, andpraseodymium, wherein M¹ and M² are different. Water is added to theanhydrous solvent to hydrolyze the first intermediate to produce aprecursor solution. The precursor solution is permitted to form a gelwherein, after gel formation, at least 90% of M¹ and M² is integratedinto the gel. The gel is formed into a nanomaterial.

In a second embodiment, a method for producing a multi-metal oxideceramic nanomaterial is disclosed. The method comprising steps of mixinga first metal-organic salt comprising a first metal (M¹), a secondmetal-organic salt comprising a second metal (M²) and a thirdmetal-organic salt comprising a third metal (M³) in an anhydrous solventto form a first intermediate, wherein M¹, M² and M³ are independentlyselected from the group consisting of barium, manganese, titanium, iron,nickel, copper, bismuth, cobalt, samarium, and praseodymium, wherein M¹,M² and M³ are different. Water is added to the anhydrous solvent tohydrolyze the first intermediate to produce a precursor solution. Theprecursor solution is permitted to form a gel wherein, after gelformation, at least 90% of M¹, M² and M³ is integrated into the gel. Thegel is sintered for a predetermined time at a predetermined temperatureto form a nanomaterial, wherein the predetermined temperature is lessthan 180° C.

In a third embodiment, a nanomaterial with a formulaBa_(A)Mn_(B)Ti_(C)O_(D) is disclosed, where A is 1 to 2, B is 2 to 4, Cis 3 to 5 and D is 12 to 18.

This brief description of the invention is intended only to provide abrief overview of subject matter disclosed herein according to one ormore illustrative embodiments, and does not serve as a guide tointerpreting the claims or to define or limit the scope of theinvention, which is defined only by the appended claims. This briefdescription is provided to introduce an illustrative selection ofconcepts in a simplified form that are further described below in thedetailed description. This brief description is not intended to identifykey features or essential features of the claimed subject matter, nor isit intended to be used as an aid in determining the scope of the claimedsubject matter. The claimed subject matter is not limited toimplementations that solve any or all disadvantages noted in thebackground.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the features of the invention can beunderstood, a detailed description of the invention may be had byreference to certain embodiments, some of which are illustrated in theaccompanying drawings. It is to be noted, however, that the drawingsillustrate only certain embodiments of this invention and are thereforenot to be considered limiting of its scope, for the scope of theinvention encompasses other equally effective embodiments. The drawingsare not necessarily to scale, emphasis generally being placed uponillustrating the features of certain embodiments of the invention. Inthe drawings, like numerals are used to indicate like parts throughoutthe various views. Thus, for further understanding of the invention,reference can be made to the following detailed description, read inconnection with the drawings in which:

FIG. 1A is a schematic illustration of two methods of producing aheterogeneous film comprising a nanomaterial;

FIG. 1B schematically illustrates control of final nanomaterialstructure by selection of metal organic salt composition;

FIG. 2A and FIG. 2B show synchrotron XRD and PDF refinement patterns ofcrystalline BaMn₃Ti₄O_(14.5) and the crystal structure, spin and chargeordering model of crystalline BaMn₃Ti₄O_(14.5), respectively;

FIG. 2C shows a lattice image by double-aberration HRTEM ofBaMn₃Ti₄O_(14.5);

FIG. 3A is a temperature dependent susceptibility plot ofBaMn₃Ti₄O_(14.25) measured at 2 kOe under FC and ZFC conditions; theinset shows inverse CFC susceptibility with a Curie-Weiss fit;

FIG. 3B is a magnetic hysteresis loops of BaMn₃Ti₄O_(14.25) at differenttemperatures;

FIG. 3C is an x-ray photoelectron spectroscopy (XPS) analysis ofBaMn₃Ti₄O_(14.25);

FIG. 3D plots resistivity as a function of temperature with differentBa:Mn:Ti ratios;

FIG. 4A depicts P-E hysteresis loops of BaMn₃Ti₄O_(14.25) with differentmaximum applied electric fields;

FIG. 4B and FIG. 4C show ferroelectric hysteresis measured in BMT-134 at100K (FIG. 4B); 120 K (FIG. 4C);

FIG. 4D was measured at 160 K showing unambiguous switching andsaturation only at a higher poling rate;

FIG. 4E shows variation in P(E) loops in the same sample using identicalvoltage sweep rate of 5 Hz; and

FIG. 4F depicts frequency dependent dielectric properties ofBaMn₃Ti₄O_(14.25) from 1-100 MHz, the inset is from 100 Hz-1 MHz at 300K together with dielectric loss.

DETAILED DESCRIPTION OF THE INVENTION

This disclosure provides an environmentally friendly synthesis methodfor forming multi-metal oxide ceramic nanomaterial, such as ananocrystal, and the multi-metal oxide ceramic nanomaterial resultingtherefrom. The method permits the synthesis of multi-metal oxide ceramicnanomaterial with tunable sizes, tunable properties, provides low energyconsumption, minimal waste, is environmentally friendly, has high yieldand the multi-metal oxide ceramic nanomaterial are easy to collect. Asused in this specification, the phrase “multi-metal” refers to three ormore different metals. The phrase “bi-metal” refers to two differentmetals.

Low temperature chemical deposition methods for preparing high qualitycrystalline oxide films are interesting for purposes of miniaturizationand integration, to serve the needs of the electronics industry. Anexample is high dielectric constant oxides, of interest for gatedielectrics, capacitor integration and on chip power design. Thisdisclosure provides a convenient and versatile method for preparingcomplex oxides using a low temperature technique referred to as“gel-collection” method, or “gel-rod” method. The gel-collection methodwas applied to the synthesis of barium, manganese, and titaniumcompositions, with the goal of introducing multifunctionality into alattice framework using Mn and Ti ions to obtain complimentary magneticand dielectric/ferroelectric properties, and potentially generatingcoupling between them. The scope is naturally not restricted to theseelements, since the possibility for intersubstitution with a variety ofmain group or transition metals, rare earths and actinides opens thefloor to a wide range of compositions, such as Fe, Ni, Cu, Bi, Sm, Pr,to name a few.

Compared to traditional sol-gel or hydrothermal methods, the uniquefeatures of the gel-collection pathway are that (i) the final productcan be controlled through selection of the type of precursormetal-organic salt and, (ii) the products after solvothermal reactionphase separate from the reagent with assembling into a oxide frameworkwith no source materials in residue (producing >99% yields. The productframework is a short-range order nanoscale metal oxide—fullycrystallized at the nanoscale, without long range densification. Thestoichiometric ratio of the final product is controllable throughappropriate molar mixing of the reactants, and the substitution anddoping concentration can be controlled precisely from the onset.Therefore, the design of new complex oxides with target crystalstructures and properties, and optimization of the properties throughsubstitution, doping and changing stoichiometric ratio is possiblethrough a very efficient pathway. Moreover, because the as-synthesizedoxide framework is a nanomaterial with short-range order and essentiallya gel/putty consistency, it allows for different potential morphologiesto be created, such as films, monoliths or rods, and composites(heterogeneous nanocomposite films 2-2, 0-0 or 3-0). See FIG. 1A. Thenanomaterial may also be subjected to hydraulic pressing and annealingto form a bulk with nanoscale grains. In another embodiment, thenanomaterial is dissolved or suspended in a carrier solution anddeposited on a substrate as a nanofilm.

In addition to the disclosed methodology, this disclosure also presentsa new class of ferroics and multiferroics based on the Hollanditestructure. Oxides of Ba, Mn, Ti are almost non-existent in nature andsynthetic processing is required. Advancing inorganic chemical synthesistechniques through the disclosed gel-rod method has provided a newregion of phase space. For example, BaMn₃Ti₄O_(14.25), prepared by thismethod is a ferroelectric, with strong experimental evidence to supportthe origin of the ferroelectricity to be an electron correlation effectbetween Mn³⁺—Mn⁴⁺. BaMn₃Ti₄O_(14.25) is a giant dielectric constantmaterial (∈_(r)˜10⁴, 1 kHz), with an unusually high dielectric constant(∈_(r)˜200) up to 100 MHz. BaMn₃Ti₄O_(14.25) is also a ferrimagnet below42K, showing antiferromagnetic ordering of the Mn³⁺—Mn⁴⁺.

Complex manganese and titanium oxide frameworks present possibilitiesfor achieving direct spin-polarization coupling due to the diversity inmagnetism of the manganses cations (S=5/2, 2 and 3/2 for Mn²⁺, Mn³⁺ andM⁴⁺ respectively), combined with the “d⁰-ness” of Ti⁴⁺ cations, whichcan facilitate long range ordering through LUMO hybridization with O 2porbitals. In nature, and excluding silicates, there are fourteen oxidesthat contain Ba, Ti, and O ions, and fifteen oxides that contain Ba, Mnand O ions (co-residing with a number of other metal cations such as Fe,Cr, V etc.). Surprisingly, there are no minerals classified as beingcomposed of exclusively Ba, Ti, Mn and O ions, despite the fact thatthese are, respectively, the fourteenth, twelfth and ninth most abundantmetals in the Earth's crust.

A series of multi-metal oxide ceramic nanomaterials are provided (see,for example, Table 1) using a gel-rod method followed by a lowtemperature sintering process. Some of the multi-metal oxide ceramicnanomaterials have shown exceptional properties such as giant dielectricconstant, ferroelectric, ferromagnetic, multiferroic, magnetocaloric andelectrocaloric effects. Because the multi-metal oxide ceramicnanomaterials are aggregate-free and uniform in size they can bedissolved into a variety of carrier solutions for making relatedembedded devices such as capacitors, gate dielectrics for field effecttransistors, memory and power storage cells, magnetocaloric andelectrocaloric refrigeration components.

TABLE 1 Exemplary complexes Ba/Ti multi-metal Fe/Ti multi-metal Co/Femulti-metal complexes complexes complexes Ni/Co multi-metal complexesBa_(1-1.12)Mn_(x)Ti_(8-x)O₁₆ Fe—Mn—Ti—O Co—Fe—Ti—O Ni—Co—Fe—Mn—OBa_(y)Sr_(1-y)Mn_(x)Ti_(8-x)O₁₆ Ni—Fe—Ti—O Co—Fe—Mn—O Ni—Co—Ti—OBaMn₃Ti₄O_(x) Ni—Co—Fe—O Ba_(1-1.12)Fe_(x)Ti_(8-x)O₁₆ BaMn₃Ti₄O_(14.25)BaMn₃Ti₄O₁₆ Ba—Co—Ti—O Ba—Ni—Ti—O Ba—Gd—Ti—O

After the gel-rod method has been performed, multi-metal oxide ceramiccomplexes are subjected to sintering to produce the multi-metal oxideceramic nanomaterials. Certain binary metal oxides (such as BaTiO₃) andsubstitutions of the pure binary metal oxides by other cations atdifferent ratios may be completely crystallized without a sinteringprocess (such as (Ba, Sr)TiO₃ and (Ba, Gd) (Ti, Zr, Hf)O₃). Manynanoscale counterparts of the widely reported binary oxide ceramics withattractive applications can be synthesized (such as, ABO₃ type—CaTiO₃,BaTiO₃, Ba_(x)Sr_(1-x)TiO₃, SrTiO₃, MnTiO₃, CoTiO₃, FeTiO₃, NiTiO₃,YTiO₃, BiFeO₃, and AB₂O₄ type—CoFe₂O₄, NiFe₂O₄, MnFe₂O₄, NiCo₂O₄) usingthe disclosed gel-rod method.

By the disclosed method, many binary metal oxide ceramics could besynthesized at low temperatures (less than 180° C.) with most formingnanomaterials. For example, BaTiO₃ (BT) or Ba_(x)Sr_(1-x)TiO₃ (BST)could be synthesized upon heating the precursor solution at 45° C. forsix hours, or at room temperature for two weeks, and as-synthesizedproducts can self-collect to form solid gel rods, which are wellseparated from the liquid phase and are completely formed by highlycrystalline BT/BST nanoparticles. The method provides almost 100% yieldof nanomaterial products that can be easily collected and purified. Zeroloss of raw materials can also be confirmed by the NMR results, whichshow that there are only the starting solvent and organic by-productresidues in the liquid solution after the reaction. Furthermore, aseries of new multi-metal oxide ceramic nanomaterials have beensynthesized based on the present gel-rod method with distinguishedproperties. For instance, Ba_(1-1.12)Mn_(x)Ti_(8-x)O₁₆ nanomaterialpossess room temperature ferroelectric properties, low temperatureferromagnetic property and giant dielectric constant up to 10⁵. Comparedto traditional solid-state calcination method, the present method hasthe advantages that, more diverse complex metal oxides with controllablesubstitution/doping and stoichiometric ratios can be obtained. The sizesof nanomaterials are uniform and tunable in a large size range (15-100nm). In one embodiment, the nanomaterials have a size between 15 nm and50 nm. In other embodiments, the nanomaterials vary in size from 1×1×1nm to 500×500×500 nm with typical sizes being 5×20×20 nm or 10×100×20nm. For making multi-metal oxide ceramics, the gel rod method followedby low temperature sintering was required. As-synthesized nanomaterialscould not only be mechanical pressed for forming polycrystalline tabletsor bulks, but also be dissolve into diverse carrier solvents to prepareprintable ink for making related embedded devices.

Exemplary Gel-Rod Method for Forming a Multi-Metal Complexes

The metals are prepared as a metal alkoxide salt or as a metal1,3-diketone salt. For example, metal isopropoxide or metalacetylacetonate which have good solubility in solvents such as methanol,ethanol, isopropanol, acetone, could be used. The metal alkoxide salt oras a metal 1,3-diketone salt are mixed together in an anhydrous solventto form a clear solution under stirring. The final nanomaterialstructures are controlled through selection of reacted metal organicsalts. For example, metal isopropoxides tend to crosslinking one oxygenatom forming corner-shared oxygen octahedral. Metal acetylacetonatestend to crosslink by sharing two oxygen atoms forming an edge-sharedoxygen octahedral. Metal acetylacetones may be selected when intendingto form an edge shared oxygen octahedral framework, such as a hollanditestructure. Isopropoxides may be selected when intending to formcorner-shared oxygen octrahedral frameworks, such as a perovskitestructure. See FIG. 1B. The solvent is anhydrous solvent to prevent thepremature hydrolysis of an intermediate that is formed. Exemplaryanhydrous solvents include anhydrous ethanol, anhydrous methanol andanhydrous isopropanol. Anhydrous solvents are generally at least 99%pure. Anhydrous solvents are substantially devoid of water such that theintermediate may be formed before its subsequent hydrolysis, therebypromoting gel formation.

Once the clear solution is formed, a predetermined percentage of wateris added. The nature of water used, and the water's predeterminedquantity, distinguishes the procedure from a variety of sol-gel orsolution processing techniques, and is advantageously to the reactionpathway. The water that is used is deionized water, and should have aconductivity of less than 0.10 μS/cm [or 0.10×10⁻⁶ S/cm)], whichcorresponds to a resistivity of greater than 10×10⁶ ohms-cm (10 MΩ-cm).The water should also be purged of (i) carbonate or bicarbonate ions(e.g. CO₃ ²⁻ or HCO₃ ⁻) or dissolved carbon dioxide (CO₂), and purged ofdissolved oxygen (e.g. O_(2(aq))). The specially treated water inpredetermined quantity permits controlled hydrolysis of theintermediate, which in turn, controls the size of the resultingmulti-metal oxide ceramic nanomaterials. Purity and composition is alsoinfluenced by the controlled hydrolysis of the intermediate. Furtherstirring forms stable precursor solution. The stable precursor solutionis left undisturbed until the stable precursor solution turns viscous.Thereafter, the stable precursor solution is heated for a predeterminedperiod of time to promote gel-rod formation. For binary metal oxideceramics, completely crystalline products could be attained attemperatures lower than 180° C. For multi-metal oxide ceramics, thegel-rod formation followed by low temperature sintering were used forconverting an amorphous phase into a crystalline phase.

The significant contributions of the disclosed method include (1) anenvironmentally friendly solvothermal process that can be applied tosynthesize a variety of complex metal oxides, and (2) the discovery of anew class of multi-metal oxides that exhibit extraordinary properties.The successful performance of the method demonstrates that low energyconsumption (lower temperature and shorter synthesis time, such as 45°C. and 6 hours) can be used for synthesizing highly crystalline andhighly pure BST or doped nanomaterials with minimum waste. Since nocatalyst or mineralizing agent are used for the reaction, themulti-metal oxide ceramic nanomaterials can self-collect to provide asolid gel-rod which is well separated from the liquid phase and iscompletely made of highly crystalline nanoparticles. The synthesisprocess provides almost 100% yield of nanomaterial products that can beeasily collected and purified.

Many unique properties, such as multiferroic property, are provided bythe multi-metal oxide ceramic nanomaterials because thesubstitution/doping to the oxide structure are flexible and could beprecisely controlled. For example, the Ba_(x)Mn_(tx)Ti_(8-tx)O_(y)material system, which exhibits both ferroelectric and ferromagneticproperties, can be used as a semiconductor for making filed effecttransistor and optical devices.

In one embodiment, a Ba_(x)Mn_(tx)Ti_(8-tx)O_(y) system is provided.Structural characterizations show the Ba_(x)Mn_(tx)Ti_(8-tx)O_(y) systemis tetragonal phase at room temperature and belongs to Hollanditefamily, which are very similar to crystal structure of Ba_(1.12)Ti₈O₁₆,where Mn⁴⁺ ions can substitute Ti⁴⁺ ions at any ratio.

Property characterization for the Ba_(x)Mn_(tx)Ti_(8-tx)O_(y) systemshows the BaMn₃Ti₄O₁₅ exhibits a variety of attractive properties suchas giant dielectric constant (up to 10⁵), room ferroelectric propertyand low temperature ferromagnetic property. Since thesubstitution/doping of the system is flexible and controllable using thepresent method, distinguished properties such as multiferroics arepromising among some Ba—Mn—Ti—O system or other multi-metal oxideceramics. For the application of printing, the best dielectricproperties (high dielectric constant and low loss) can be achieved fromthe dropcast composite film of BaMn₃Ti₄O₁₆ nanomaterials and PVDF-HFPwhich, to date, produces the best dielectric properties compared toreported similar 0-3 type composite films.

BaMn₃Ti₄O_(14.25)

Using the gel-collection method, and reactants in molar composition1:3:4, a complex oxide based on Ba/Mn/Ti was prepared. A single phaseproduct, a new compound, was readily isolated and identified. Thecrystallites were studied extensively by synchrotron X-ray diffractionhigh resolution transmission electron microscopy (FIG. 2A). In FIG. 2A,line 200 is calculated PDF, lin3 202 is experimental PDF and line 204 isthe difference. In summary, a new compound that comprises both Ti and Mnions was prepared, with the specific formula BaMn₃Ti₄O_(14.25). Thestructure belongs to the Hollandite supergroup, A^(II)[M^(IV),M^(III)]O₁₆. The combined presence of Mn and Ti cations allows thematerial to present a variety of unique physical properties as aconsequence of electrical polarization, magnetic polarization, and theinteraction between the two. FIG. 2B depicts the crystal structure, spinand charge ordering model of BaMn₃Ti₄O_(14.25).

Synchrotron X-ray powder data was collected for Pairwise DistributionFunction analysis, PDF. The refinement results show that the compoundsclosely resemble the redledgeite structure (space group 79, I4). The Baatoms have local distortions along the z-axis, since a fraction of theBa atoms are sitting off their equilibrium sites, which is only obviousat low-r range (<20 Å). The Mn and Ti cations are located inside cornerand edge-shared oxygen octahedra. Double aberration corrected HRTEMclearly shows the hollandiate type lattice, looking down the channels.There is a small (˜6°) lattice rotation (FIG. 2C), attributed to localdisorder. XPS analysis confirms the presence of stable Ti⁴⁺ and mixedMn³⁺ and Mn⁴⁺ cations. No Ti⁴⁺ or Mn²⁺ is detected. In combination withthe PDF refinement, the EDX, EELS and XPS analysis, all corroborate themetal cation Ba:Mn:Ti stoichiometric ratio to be 1:3:4, identical to theinitial reactant concentration.

Temperature dependent DC magnetic susceptibility (FIG. 3A) showsparamagnetic behavior from 120-300 K, and antiferromagnetic orderingaround 42 K (T_(N)). The paramagnetic behavior fits classicalCurie-Weiss law behavior (inset of FIG. 3A), χ(T)=C/(T−θ), with C=2.44and θ=−107. The estimated effective moment per Mn cations, 4.4μ_(B),further confirms the presence of Mn³⁺ and Mn⁴⁺ cations with a ratio of1:1. Hence, the stoichiometry of the oxide is confirmed asBaMn₃Ti₄O_(14.25), consistent with structure refinement, valence andmagnetic analysis. The oxide presents ferrimagnetic behavior below T_(N)(FIG. 3B), ascribed to the effective moments of Mn³⁺ and Mn⁴⁺ orderingantiferromagnetically, resulting in a net moment. The saturationmagnetization at 1.84K is ˜1μ_(B), equal to difference between Mn³⁺ andMn⁴⁺ moments and implies a pair distribution within the lattice. Interms of super-exchange of Mn⁴⁺—Mn⁴⁺ and Mn³⁺—Mn³⁺, the stable spinconfiguration of Mn⁴⁺ and Mn³⁺ is depicted in FIG. 2B, consistent withpreviously reported Hartree-Fock calculations. FIG. 3C is an x-rayphotoelectron spectroscopy (XPS) analysis indicating evidence of Mn³⁺and Mn⁴⁺ and no evidence of Mn²⁺. FIG. 3D is a plot of resistivity as afunction of temperature ρ(T) in samples of (Ba—Ti—Mn—O) with differingBa:Mn:Ti ratios: line A: 1:2:5 (BaMn₂Ti₅O_(14.5)), line B: 1:3:4(BMT-134), and line C: 1:4:3 (BaMn₄Ti₃O₁₄). The dramatic change incharacter of ρ(T) in the case of BMT-134 provides additional evidence ofthe potential onset of a charge-ordering transition near 120K.

The BaMn₃Ti₄O_(14.25) composition is a multiferroic. One excitingdiscovery of BaMn₃Ti₄O_(14.25) is that of room temperatureferroelectricity. Generally, Mn³⁺—Mn⁴⁺ mixed valence oxides exhibit alarge electrical conductivity, and would inhibit generation of localizedpolarization or mask any evidence of ferroelectric hysteresis. Using aSawyer-Tower/parallel-plate device configuration, ferroelectrichysteresis loops are observed (FIG. 4A). Typical leakage loops areobserved for an applied electric field <600 kv/cm. Above this criticalvalue, a transition to a crisp ferroelectric loop with remnantpolarization is observed. The leakage type loop for <600 kv/cm isinterpreted as due to the presence of mixed valence Mn³⁺—Mn⁴⁺. Thepossibility of ferroelectricity due to Schottky contacts and or spacecharge was unequivocally excluded through C-V analysis. Ferroelectricityin BaMn₃Ti₄O_(14.25) can be ascribed to a field induced phase change byelectron correlation of charge ordering. Based on the refined averagestructure of BaMn₃Ti₄O_(14.25), covalent Ti—O bonds (Ti—O distance inrange of 1.9-2 Å) could distort to form dipoles. This would create analternating chain of anti-parallel dipoles from the to Ti cationneighboring edge-shared oxygen octahedron, which would result in netpolarization of zero. Combined with the observation that thisfield-induced behavior occurs >600 kV/cm, we conclude that the origin ofremnant polarization as being due to a displacive transition isunlikely. FIG. 4B, FIG. 4C and FIG. 4D show ferroelectric hysteresismeasured in BMT-134 at 100K (FIG. 4B); 120 K (FIG. 4C), each at a 5 Hzpoling rate, exhibiting ferroelectric switching and saturation at 120 K.FIG. 4D was measured at 160 K showing unambiguous switching andsaturation only at a higher poling rate due to stronger charge leakage.FIG. 4E shows variation in P(E) loops in the same sample using identicalvoltage sweep rate of 5 Hz, indicating an onset of leakage at thispoling rate with temperature above about 150 K, below whichferroelectric switching and polarization saturation is observed. At 100K and below, the value of saturation polarization for a given appliedfield is seen to decrease for decreasing T, presumably due toapplication of an insufficiently large field and incomplete poling,consistent with Landau theory for a displacive transition.

Two key structure factors make the hypothesis of electron correlationferroelectricity credible: first, the Mn³⁺ and Mn⁴⁺ do not coincide inthe unit cell (they are separated by a chain of edge-shared TiO₆octahedra, see FIG. 2B) such that an asymmetric response to the electricfield is expected (generation of electrical polarization originatingfrom the electron density modulation). Second, because the structurepossesses an insulating layer of TiO₆ octahedra that separates the Mn³⁺and Mn⁴⁺ ions—a barrier by which electron transfer is restricted—therewould be stabilization of the localized polarization state. Sufficientlyhigh electric DC fields causes the unit cell to extend along the [110]direction due to electron density modulation with a polarization in thisdirection, and such a modulation would be accompanied by a latticerotation (FIG. 2B). BaMn₃Ti₄O_(14.25) presents a giant dielectricconstant (FIG. 4F): the dielectric constant is >10⁵ at low frequencies,>10⁴ up to 1 kHz, >10³ up to 1 MHz, and, perhaps most interestingly,remains high, >200 up to 100 MHz and beyond (DF<0.1, FIG. 4B inset). Thehigh permittivity is attributed to electron related polarization inconjunction with electron correlation polarization playing key role inthe ferroelectric behavior of BaMn₃Ti₄O_(14.25). A new type chargeordering ferroelectricity by field induce was achieved based on newdesigned and synthesized BaMn₃Ti₄O_(14.25).

In summary, a new multiferroic complex oxide with the formulaBaMn₃Ti₄O_(14.25) was identified. The structure belongs to thehollandite supergroup family. The ability to design and synthesizesynthetic minerals with multiferroic properties via a novel chemicalmethod, the gel-collection (gel-rod) method, illustrates the power andcontrol of this precursor based inorganic synthesis technique in thesearch for new oxides with magnetoelectric properties. BaMn₃Ti₄O_(14.25)demonstrates ferroelectricity that is field induced. The origin of theferroelectricity is attributed to an electron correlation polarizationeffect.

Methods

Synthesis of oxide frameworks and related nanomaterials: The complexoxide framework rod/cube can be prepared by the gel-collection method.Metal isopropoxide or acetylacetonate, which can solve into the solventssuch as methanol, ethanol, isopropanol, acetone, could be raw materials.In a typical synthesis, for example BaMn₃Ti₄O₁₄ oxide framework, bariumisopropoxide, manganese acetylacetonate and titanium isopropoxide weremixed together in pure ethanol with atomic ratio 1:3:4; after formingclear and transparent solution with magnetic stirring, transfer thesolution to autoclave and heated to 100-200° C. above 24 h. Furthersintering the rod/cube around 700° C., pure BaMn₃Ti₄O₁₄ nanomaterialswere obtained.

Synchrotron radiation XRD and PDF refinement: X-ray powder diffractionexperiments were performed at X17A beamline at National SynchrotronLight Source (NSLS) Brookhaven National Laboratory. Date were collectedat room temperature with an X-ray energy of 67.557 keV (λ=0.1839 Å)using Rapid acquisition pair distribution function (RAPDF) technique.The 2D detector was used in data collection with a sample to detectordistance of 204.067 mm, which is calibrated using a silicon standardsample. The scattering signal from empty kapton tube was measured andsubtracted as a background. 2D diffraction patterns were integrated to1D diffraction intensity in q-space using homemade SrXplanar program andtransformed to PDF using PDFgetX3. Experiment PDF was obtained using asine Fourier transformation of powder diffraction data according to

$\begin{matrix}{{{G(r)} = {\frac{2}{\pi}{\int_{Q_{\min}}^{\infty}{{Q\left\lbrack {{S(Q)} - 1} \right\rbrack}\sin\;{Qr}\ {\mathbb{d}Q}}}}},} & (1)\end{matrix}$where Q is the magnitude of scattering vector and S(Q) is the totalscatting structure function. The PDF can be calculated using,G(r)=4πr[ρ(r)−ρ₀],  (2)where r is the radial distance, ρ(r) is the atomic pair-density atdistance r, ρ₀ is average atomic number density. The agreement ofexperiment PDF and calculated PDF is characterized by residual function,

$\begin{matrix}{{R_{w} = \sqrt{\frac{\sum\limits_{i = 1}^{N}\;\left\lbrack {{G_{obs}\left( r_{i} \right)} - {G_{calc}\left( {r_{i};\overset{\rightarrow}{P}} \right\rbrack}^{2}} \right.}{\sum\limits_{i = 1}^{N}\;{G_{obs}^{2}\left( r_{i} \right)}}}},} & (3)\end{matrix}$where G_(obs) is the experimental PDF, G_(calc) is the calculated PDFfrom the model and {right arrow over (p)} is the list of refinableparameters in the model.

Atomic-resolution TEM: Samples for STEM and EELS were prepared bydepositing dilute nanomaterial in ethanol solutions on ultrathin carbongrids. We used JEOL ARM 200CF equipped with a cold field-emission gunand double-aberration correctors at Brookhaven National Laboratory. AllSTEM and EELS were performed with 200 kV electrons. The acceptanceangles for high-angle annular-dark-field (HAADF) detectors were from 68to 280 mrad. The energy resolution for EELS was about 0.5 eV with 0.25eV/ch dispersion.

XPS characterization: XPS analyses were carried out with ESCA⁺ systemusing a Al KR source (1386.6 eV). The powder of BaMnTiO were mounted onnon-conductive adhesive tape of stainless steel sample holder. The basepressure of the deposition chamber was 1×10⁻⁹ Torr. The survey spectrain the range of 0-1386.6 eV were recorded in 0.1 eV step for the sample,curve fitting was performed after a Shirley background subtraction by aLorenzian-Gaussian method.

Electric and magnetic properties measurement: The magnetic properties ofnanomaterials were measured by Magnetic Properties Measurement System(MPMS, Quantum Design). The sandwich type devices were made by spincoating BaMn₃Ti₄O₁₄ nanomaterials (carrier solvent, ethanol) betweenelectrodes, and ferroelectric properties of them were tested by thePrecision Workstation (Radiant Technology). Four-point DC temperaturedependent conductivity were measured on BaMn₃Ti₄O₁₄ tablets by PPMS.Frequency dependent dielectric properties of BaMn₃Ti₄O₁₄ tablets weremeasured by LCR Meter (Agilent, 4980A) and Impedance Analyzer (Agilent,E4991A).

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal language of the claims.

What is claimed is:
 1. A method for producing a multi-metal oxideceramic nanomaterial, the method comprising steps of: mixing a firstmetal-organic salt comprising a first metal (M¹), a second metal-organicsalt comprising a second metal (M²) and a third metal-organic saltcomprising a third metal (M³) in an anhydrous solvent to form a firstintermediate, wherein M¹, M² and M³ are independently selected from thegroup consisting of barium, manganese, titanium, iron, nickel, copper,bismuth, cobalt, samarium, and praseodymium, wherein M¹, M² and M³ aredifferent; adding deionized water to the anhydrous solvent to hydrolyzethe first intermediate to produce a precursor solution; permitting theprecursor solution to form a gel wherein, after gel formation, at least90% of M¹, M² and M³ is integrated into the gel; sintering the gel for apredetermined time at a predetermined temperature to form ananomaterial, wherein the predetermined temperature is less than 180° C.2. The method as recited in claim 1, wherein M¹, M² and M³ areindependently selected from the group consisting of barium, titanium anda third metal selected from the group consisting of manganese, iron,nickel, copper, bismuth, cobalt, samarium, and praseodymium.
 3. A methodfor producing a multi-metal oxide ceramic nanomaterial, the methodcomprising steps of: mixing a first metal-organic salt comprising afirst metal (M¹), a second metal-organic salt comprising a second metal(M²) and a third metal-organic salt comprising a third metal (M³) in ananhydrous solvent to form a first intermediate, wherein M¹, M² and M³are independently selected from the group consisting of barium, titaniumand manganese, wherein M¹, M² and M³ are different, such that thenanomaterial has a formula Ba_(A)Mn_(B)Ti_(C)O_(D), where A is 1 to 2, Bis 2 to 4, C is 3 to 5 and D is 12 to 18; adding water to the anhydroussolvent to hydrolyze the first intermediate to produce a precursorsolution; permitting the precursor solution to form a gel wherein, aftergel formation, at least 90% of M¹, M² and M³ is integrated into the gel;sintering the gel for a predetermined time at a predeterminedtemperature to form a nanomaterial, wherein the predeterminedtemperature is less than 180°.
 4. A method for producing a multi-metaloxide ceramic nanomaterial, the method comprising steps of: mixing afirst metal-organic salt comprising a first metal (M¹), a secondmetal-organic salt comprising a second metal (M²) and a thirdmetal-organic salt comprising a third metal (M³) in an anhydrous solventto form a first intermediate, wherein M¹, M² and M³ are selected fromthe group consisting of barium, titanium and manganese, wherein M¹, M²and M³ are different, such that the nanomaterial has a formulaBa_(A)Mn₃Ti₄O_(D), where A is 1 to 1.12 and D is 14.25 to 16; addingwater to the anhydrous solvent to hydrolyze the first intermediate toproduce a precursor solution; permitting the precursor solution to forma gel wherein, after gel formation, at least 90% of M¹, M² and M³ isintegrated into the gel; sintering the gel for a predetermined time at apredetermined temperature to form a nanomaterial, wherein thepredetermined temperature is less than 180°.
 5. The method as recited inclaim 4, wherein D is about
 16. 6. The method as recited in claim 4,wherein D is about
 14. 7. A method for producing a multi-metal oxideceramic nanomaterial, the method comprising steps of: mixing a firstmetal-organic salt comprising a first metal (M¹), a second metal-organicsalt comprising a second metal (M²) and a third metal-organic saltcomprising a third metal (M³) in an anhydrous solvent to form a firstintermediate, wherein M¹, M² and M³ are independently selected from thegroup consisting of barium, manganese, titanium, iron, nickel, copper,bismuth, cobalt, samarium, and praseodymium, wherein M¹, M² and M³ aredifferent; adding water to the anhydrous solvent to hydrolyze the firstintermediate to produce a precursor solution; permitting the precursorsolution to form a gel wherein, after gel formation, at least 90% of M¹,M² and M³ is integrated into the gel; sintering the gel for apredetermined time at a predetermined temperature to form ananomaterial, wherein the predetermined temperature is less than 180°C., wherein the nanomaterial is a mixed metal oxide of the Hollanditesupergroup structure type of the formula M¹M²M³O_(z) where z is 12 to18.
 8. The method as recited in claim 7, wherein M¹ is Ba, M² is Mn, M³is Ti such that the formula is Ba_(A)Mn_(B)Ti_(C)O_(z), where A is 1 to2, B is 2 to 4, C is 3 to 5 and Z is 12 to
 18. 9. The method as recitedin claim 8, wherein A is 1 to 1.12, B is about 3, C is about 4 and Z isabout 14 to
 16. 10. The method as recited in claim 8, wherein A is 1 to1.5, Z is 14 to
 16. 11. The method as recited in claim 8, wherein thenanomaterial has a dielectric constant of greater than 10⁴ at 1 kHz andgreater than 200 at 100 MHz.
 12. The method as recited in claim 1,wherein the deionized water has a conductivity of less than 0.10 μS percm.
 13. The method as recited in claim 1, wherein the deionized waterhas been purged of bicarbonate ions, carbon dioxide and oxygen.